The present invention relates to a process and to a plant for producing pressurized air gases by cryogenic air distillation.
Certain (type 1) processes, such as those described in EP-A-0 504 029, produce oxygen at high pressure (>15 bar) using a single compressor to compress the air to a pressure well above the pressure of the medium-pressure column.
These processes are suitable for a context in which investment costs are of prime importance, as they have the drawback of consuming a very large amount of energy when no liquid production is required.
Other (type 2) processes, using a high air pressure only for producing pressurized gaseous oxygen, are disclosed in U.S. Pat. No. 5,475,980 and have a better specific energy for producing gaseous oxygen at high pressure, without producing liquid (or with a low production of liquid). They use cryogenic compression of air pressurized by means of a blower mechanically linked to an expansion turbine.
However, this energy advantage is counterbalanced by an investment substantially greater than that of type 1, as this is an expensive process in terms of exchanger volume. This is because in general a large fraction (60% to 80%) of the main air stream undergoes adiabatic cryogenic compression before being reintroduced into the main exchange line.
Finally, these types of process seem to be economically advantageous, and the choice will depend on the intended utilization of the energy, available at low or high cost.
In this document, the term “condensation” includes pseudo-condensation and the term “vaporization” includes pseudo-vaporization.
Temperatures are considered as being similar if they differ by at most 10° C., preferably at most 5° C.
The exchange line is the main exchanger where the gases produced by the column system are warmed and/or where the air intended for distillation is cooled.